In recent years the concern for protecting our environment has grown considerably. The United States, as a country, has become very interested in protecting wildlife, forests, both above and below ground water resources and in improving our air quality.
There are many sources of air pollution which contribute to the overall pollution problem Factory emissions, automobile and truck emissions and fluorocarbons emissions are the most common type of air pollutants. Aromatic emissions from liquid hydrocarbon fuels are another type of air pollutant. A typical source of aromatic pollution originates from the transfer of these liquid fuels from one storage tank to another. Filling an empty storage tank with fuel causes the air inside to be displaced by the liquid pouring in. When this occurs, the air mixes with the fuel and becomes vaporous, being forced out of the tank. This fuel laden vapor mixes with the atmosphere and forms part of the soup called air pollution.
A typical instance of fuel transfer can be found at a truck or automobile service station. There are two types of fuel transfer which occur at service stations, both of which have recently come under regulation. The first type of fuel transfer is from a delivery tanker truck directly into a below or above ground bulk fuel storage tank. This bulk transfer fuel is now regulated under what is called "Stage I Vapor Recovery" which requires an approved means of recovering all of the vapors escaping from the storage tank and transferring them into the bulk fuel delivery truck or tanker truck that is pumping the liquid fuel. This type of system requires that a vapor hose interconnect the tanker truck and the storage tank.
The second type of fuel transfer is from the storage tank to the vehicle tank located on a truck or automobile. This transfer typically requires the use of an underground piping system interconnecting the storage tank and one or more above ground fuel dispensers that meter the amount of liquid fuel transferred. The fuel may be pumped from the storage tank to the dispenser by means of a submersible pump or fuel pump located at the tank. Alternatively, fuel may be suctioned from the storage tank to the dispenser by means of a suction pump located within the dispenser. This transfer fuel is now regulated under what is called "Stage II Vapor Recovery," which requires an approved means of recovering all of the vapors escaping from the vehicle tank and transferring them into the storage tank from which the liquid fuel is being pumped or suctioned by the fuel pump.
The invention relates to the second type of vapor recovery system called Stage II Vapor Recovery. There are a number of approved Stage II Vapor Recovery systems on the market and in use which attempt to recover the fuel vapors which escape the vehicle tank during refueling. All of these systems require a dedicated piping line from the dispenser back to the bulk storage tank. Another requirement is to have a special filling nozzle which provides a vacuum inlet with an attached dedicated return vapor hose for interconnecting the nozzle to the vapor piping located just under the dispenser.
The types of Stage II Vapor Recovery Systems which are approved and available can be classified into two distinct groups. The first group, which most commonly used, are "balanced systems" which use the vacuum created by the displacement of fuel in the storage tank, during pumping, as a means of recovering the vapors being forced out of the vehicle tank and back to the storage tank. The second group are "power assisted systems" which create a vacuum by means of a powered vacuum pump as a means of recovering the vapors being forced out of the vehicle tank during filling. Because power assisted systems are not inherently balanced systems, there exists a concern that the vacuum pumps will not create sufficient vacuum to recover all of the vehicle tank vapors or, alternatively, will cause too much vacuum causing the storage tank to have a positive pressure. This positive pressure will result in the tank venting vapors into the atmosphere through the storage tank's vent lines. To prevent this from occurring power assisted systems have additional mechanical controls and devices to prevent aromatic vapor discharge into the atmosphere through the vent stack.
The balanced system, which is the most commonly used system on the market, is difficult to install properly and does not recover 100% of the vehicle tank's vapor emission back to the storage tank. This system requires that a rigid type vapor piping system be installed which maintains slope (1/8" fall per lineal foot minimum) from each dispenser back to a storage tank typically installed underground. The sloped vapor piping line allows condensed fuel to drain to the storage tank. Flexible pipe would inevitably trap liquids at low points in the path.
Sometimes, particularly in warm weather where the vehicle tank may be at 85.degree. to 95.degree. F., aromatic vapors which are vacuumed out of the vehicle tank may partially condense when they are exposed to the cooler underground vapor piping at 55.degree. F. ground temperature. It is for this reason an adequate slope must be maintained by the rigid vapor piping line so that unrestricted flow will occur all the way to the storage tank. Typically, a 2" or 3" line is installed to provide adequate sizing to compensate or dips and rises in the rigid vapor piping line due to ground settling or improper installation. In some cases where there is not sufficient fall available from the dispenser back to the storage tank, a drop-off tank is installed in the vapor piping line to trap and collect liquid fuel and to create additional fall.
It should be noted that larger diameter vapor piping lines use a slower velocity of air flow. This slower air flow combined with more piping surface area creates a large volume of liquid fuel which can collected through condensation. This is not a problem as long as proper slope is maintained but in practice does cause difficulty in service.
The balanced system uses a combination of a positive and negative atmospheric pressure, as well as gravity, to transfer the vapors from the vehicle tank to the underground storage tank. As previously discussed, the "negative pressure" or vacuum is created by the displacement of fuel leaving the storage tank and the "positive pressure" is created by the fuel being pumped into the vehicle tank. In order to insure that virtually all (99.5% is the present requirement) of the aromatic vapors escaping the vehicle tank are suctioned into the vacuum openings in the nozzle it is necessary to have a rubber boot on the outside of the nozzle to seal the opening in the vehicle tank from the outside atmosphere. This rubber boot creates a direct sealed connection between the nozzle and the opening of the vehicle tank. This seal connection prevents any positive pressure from escaping into the atmosphere from the vehicle tank and prevent outside air from being sucked in by the nozzle.
The problem with the nozzle fitted with a rubber boot is that it is very cumbersome for the customer who is filling the vehicle tank. Additionally, "topping-off the tank" (adding more fuel after the nozzle automatically trips) is not permitted or recommended, creating a lot of loose change for cash customers. Another problem is that worn rubber boots may loose their effectiveness in making a good vacuum seal to ultimately make the balance system less effective.
Another problem with balanced systems is that they require sufficient slope of the vapor piping line from all dispensers to a low point just above the lop of the underground storage tanks. This means that the top of the underground storage tank must be at least 36 inches from the ground surface and in many cases much deeper. This deeper tank burial requirements more costly excavations and additional backfill materials such as pea gravel which can be very expensive. For existing service station sites which are being retro-fitted with Stage II Vapor Recovery Systems this could require that the tanks be removed and buried deeper to maintain proper fall or that in-line drop-off tanks be installed that require constant emptying and maintenance.
Balanced Stage II Vapor Recovery Systems are also very time consuming to install because they require the use of steel or fiberglass rigid piping for the vapor piping lines. In many areas regulators require that the vapor piping be secondarily contained which will more than triple the cost of the vapor piping. Many service stations today are using environmentally safe flexible double wall fuel piping systems. These flexible piping systems are available in long rolls providing continuous piping runs, unlike rigid piping systems which require many piping joints for straight piping connections and directional fittings. One other disadvantage of rigid vapor piping lines is that it can not be routed exactly adjacent to the flexible piping lines because the directional fittings are typically very sharp (90.degree. and 45.degree. turns) and the rigid pipe will obviously not bend to the same extent that flexible piping will.
One type of "Power Assisted Stage II Vapor Recovery System" called the Heally System operates as fellows. The Heally System consists of a nozzle which provides for return hydrocarbon vapor from the vehicle tank through a rubber boot, back to the storage tank. The vapor is subjected to a vacuum source in the nozzle which is created by a liquid gasoline driven jet pump. When the pump switch is activated, gasoline under pressure is provided to the jet pump. A small stream of gasoline diverted from a point ahead of the meter, flows through the jet point and back to the underground storage tank. Vacuum is immediately produced at a controlled maximum level of-24 to -30 inches of water column. When the nozzle is in use, the vapors are recovered through the jet pump and returned to the gasoline storage tank.
One of the difficulties of these type of pumps is that the return of vapor and gasoline to the storage tank will build up pressure in the storage tank, thereby blowing vapor out of the vent stack at the station. While the system may operate normally for a one pump system, typically, the average service station has anywhere from one to twelve or more nozzles operating at the same time. It is extremely difficult to regulate the vacuum over the range required to give the appropriate vacuum without putting excessive pressure on the venting means. The undesirable alternative is to burn off excess vented vapors which is both wastefull and potentially hazardous.
The Hasstech Stage II Vapor Recovery System, manufactured by Hasstech, Inc. of San Diego, provides a vacuum assist created by a central vacuum pump connected to all dispensers. Holes near the tip of the nozzle create a zone of flow pressure in the fill neck which collect the displaced gasoline vapors and prevent them from escaping into the atmosphere. This and other systems using a vacuum assisted vapor recovery system have to date only been able to recover 95% of secondary vapors in the vehicles fuel tanks. All such systems also require that excess vapors be processed for combustion in an on site processing unit.
None of the prior art systems effectively provide a system for dispensing fuel from storage tanks to vehicle fuel tanks without at least some of the vapors escaping from the vehicle tank. Accordingly, it is an object of this invention to provide a system that recovers substantially all of the vapors escaping from a vehicle tank and transfers those vapors to a storage tank of equal or lesser octane rating.
Another object of the present invention is to provide an improved, more efficient power assisted stage II vapor recovery system.
Yet another object of the present invention is to provide such a power assisted system which avoids the need for venting or burning recaptured vapor.
Still another object of the present invention is to provide a power assisted stage II vapor recovery system which is at least 99.5% effective.
Other objects will appear hereinafter.